Protective device



March 17, 1925.

E. E. F. ,CREIGHTION PROTECTIVE DEVICE Filed March 19. 1924 InventorHisAtt ElmerEF C jghton,

orney.

Patented Mar. 17, 1925.

UNITED STATES ELMER E. F. CREIGHTON, OFSCHENECTADY, NEYV YORK, ASSIGNORTO GENERAL ELEC- vTRIO '-(JOIVIPANY, A. CORPORATION OF NEW'- YORK.

PROTECTIVE DEVICE.

Application filed March 19, 1924.. Serialv No. 700,419.

' To all whom it may concern:

.ron, acitizen of the United States, residing at Schenectady, .in thecounty of Schenectady, State of New York, have invented certain new anduseful Improvements in Protective Devices. of which'the following is aspecification.

My invention relates to protective devices or systems, and has for itsobject the provision of an improved device of this character which isreliable in operation.

The fuse, which is one of the earliest de vices used to protect electriccircuits, is now manufactured in a variety of forms which have becomemore or less standard. Among them may be mentioned the expulsion fuse,the filled tube fuse, and the open air fuse. In its common forms,however, the fuse has the disadvantage that it is not entirely reliable.in operation. This is due largely to the fact that a momentary overloadmay decrease the sectional area of the fusible element and thereby causeit to fail under normal operation conditions.

In the case of the expulsion fuse, it is common practice to make thecontainer of strong fiber or the like because of the fact thatnon-carbonaceous materials, such as porcelain, have insufficientstrength to withstand the pressure generated by vaporization of thefusible element. IVith this construction, the fiber container is apt tocarbonize on its inner surfaces thereby forming a more or lessconductive path in shunt to the fusible element. hen this occurs thefuse cannot be relied upon to interrupt the circuit.

The filled tube fuse comprises a container in which is placed a fusibleelement surrounded by a filler such as pellets of plaster Paris andslaked lime. The effectiveness of this filler depends to a large extenton its moisture content which is utilized to absorb the heat of themetal vapor and to quench the are which follows melting of the fusibleelement. This construction is objectionable in that a very heavyoverload is required to vaporize'the fusible element if its energy lossunder normal conditions is made low enough to leave the moisture of thefiller unaffected.

In accordance with my invention a plurality of fusible elements, such aswires or thin strips of metal, normally in parallel relationship witheach other are, connected in series with the circuit to be protectedandmeans responsive to excess current in the circuit are provided forchanging the connection of these elements from parallel to series. Underthese conditions the fusible elements are maintained cool under normalconditions but are suddenly melted or vaporized when the circuit istraversed by current of a predetermined higher value.

My invention will be better understood from the following descriptionwhen considered in connection withthe accompanyingdrawing, and its scopewill be pointed out in the appended claims.

The single figure of the drawing schematically shows a plurality offusible elements 1. 2,,and 3 surrounded by insulating tubes 4, 5 and 6,which may contain a suitable filler-if desired. These tubes may besupported in any convenient manner. The fusible element 1 is shown asconnected between conducting members 7 and 8, the fuse 2 as connected.between conducting members 7 and 9, and the fuse 3 as connected betweenconducting members 9 and 10. A contact member 11 controlled by thearmature 12 of an electromagnet 13 is arranged to interconnect themembers 7 and 10. A contact member 16 for interconnecting the members 8and 9 is controlled by the armature 15 of the electromagnet 14. Thearmatures 12 and 15 are illustrated as provided with springs 17 and 18respectively for biasing them to positions in which the contacts 11 and16 are closed. The operating coils 19 and 20 of the electromagnets '13and '14 are adapted to be interconnected with an electric circuitthrough leads 21 and 22 respectively.

It will be apparent that in the illustrated closed position of thecontacts 11 and 16 the fuse wires 1, 2 and 3 are connected in parallelbetween the leads 21 and 22. lVhen the contacts 11 and 16 are moved totheir open position due to excessive current in the coils 19 and 20,however, fuse wires 1, 2 and 3 are connected in series between loads 22and 21. Under these conditions the entire current traverses each wireand the energy consumed in heating the wires is suddenly increased inthe ratio of 1 to 9. It is thus possible to operate the fuse'wires at alow temperature under normal load conditions and to heat them suddenlyto the point of melting or vaporization when the circuit is traversed bya current of predetermined value. Obviously the number of fuse wires maybe made larger to increase the difference between the amount of energyconsumed in heating them under normal load conditions and that likewiseconsumed when an overload occurs and the coils 19 and are energized tomove contacts 11 and 16 out of engagementwith the cooperating stationarycontacts. 7

This method of normally operating the fuses at a low temperature andsuddenly in- 'creasing their temperature when an overloadoccurs has anumber of advantages.

Due to thesudden increase in the current carried bythe various fusibleelements it is feasible to make them of highly conductive, high'inelting point, metals such as copper or aluminum.- Thehigherconductivity of these metals permits the use of a smaller mass ofmetal with a consequent reduction in the quantity of vapor required tobe cooled. Also when a filler is used its moisture co'nten tis sobriefly in contact with hot metal'that it is practically unaffecteduntil brought into action to extinguish the are which follows themelting of the fuse.

lhe electromagnets 13 and 14 may be arranged to operate instantaneouslyin re sponse to a predetermined value of current, or may be adapted tooperate as definite or inverse time element relays.

intended to cover all changes and modifica- I,

tions within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. A system of the classdescribed comprising a plurality oflfusibleelements normally connected in parallel, relatively movable conductorsfor controllin the connections of said elements, and means for producingrelative movement between said conductors to connect said elements inseries with one another when they are traversed by current in excess ofa predetermined value.

2. In a system for protecting an electric circuit, the combination of aplurality of fusible elements, a plurality of stationary conductors forconnecting said elements in series with one another, a plurality ofmovable conductors for interconnecting said stationary conductors toconnect said elements in parallel with one another, and currentresponsive means for moving said movable conductors out of contact withsaid stationary conductors when said ele ments are traversed by currentin excess of a predetermined value.

A device of the class described comprising a plurality of fusibleelements normally connected in parallel, and means for causing saidelements to be connected in series with one another.

4. A device of the class described comprising a plurality of fusibleelements normally connected in parallel, and means for causmg saidelements to be connected inseries when they are traversed by current inexcess of a predetermined value.

5. A protective system comprising a plurality of fusible elementsnormally connected in parallel, contact members for causing saidelements to be connected in series, and electro-responsive means foroperating said contact n iembers when said elements are traversed bycurrent in excess of a prede w my hand this 18th day of March 1924.

ELMER E. r. CREIGHTON.

